1. Field of the Invention
The present invention relates to therapeutic methods for the treatment of fatty tissue deposits and alcohol-related liver degeneration. More particularly, the present invention relates to the treatment of these conditions using a particular group of compounds, the dimethylxanthines, and bioactive-equivalent derivatives thereof. The present invention also relates to compounds which alter lipid metabolism, and which possess therapeutic value in the treatment, prevention and reversal of liver degeneration and fatty tissue deposits.
The present invention also relates to therapeutic methods for reducing and/or reversing atheromatous lesions. The present invention also relates to therapeutic methods effective in the treatment, prevention and reversal of cirrhosis of the liver.
2. Description of the Related Art
Medical science has recognized a number of diet induced pathological changes in humans which result from excess alcohol or fat (i.e., cholesterol) ingestion. High cholesterol diets have been associated with disease of the large arteries, such as cardio-vascular disease. Complications of cardiovascular disease are the major cause of death in most industrialized countries, and atherosclerosis is the primary process associated with this high mortality. This disease of the large arteries has increased markedly over the past decade, making the creation of methods for its prevention and treatment a critical challenge to the medical community. The American Heart Association reports that approximately 65 million Americans suffer from serious vascular disease, while alcoholism, with its concomitant syndromes of fatty liver disease and cirrhosis, evidencing an equally grim frequency.
The epidemic proportion of reported cases of serious vascular (i.e. cardiovascular) disease and liver disease related to high-cholesterol and/or alcohol intake has raised general public awareness of these conditions and measures which may be taken to attempt their control.
Chronic ingestion of ethanol or of toxic doses of various chlorinated hydrocarbons are known to cause liver degeneration (fatty liver) and cirrhosis in man.sup.3,5 and in experimental animals.sup.1-3. These and related conditions caused by chronic alcohol consumption cause a reported 10 million cases of advanced alcoholism disease in the United States alone. Associated with chronic alcoholism is excessive mobilization of lipids and the ultimate development of a fatty liver.
The mechanism of production of fatty hepatosis is not entirely clear, but appears to be a combinaticn of several factors, such as sparing action of ethanol oxidation on utilization of liver triacylglycerols, excessive mobilization of triacylglycerols from adipose tissue to the liver caused in part by action of ethanol in triggering release of hormones, and failure to synthesize sufficient lipoprotein for transport of triacylglycerols because of alterations of amino acid availability.
The condition of cirrhosis of the liver relates to a group of chronic diseases of the liver characterized pathologically by the loss of the normal microscopic hepatic lobular architecture, with fibrosis and by destruction of parenchymal cells and their regeneration to from nodules. The disease has a lengthy latent period, usually followed by the sudden appearance of abdominal swelling and pain, hematemisis, dependent edema, or jaundice.
Fatty cirrhosis, more particularly, is characterized by the type of cirrhosis in which liver cells are infiltrated with fat (triglycerides), the infiltration usu-ally being due to alcohol ingestion.
Currently, cirrhosis has been clinically managed through the treatment of the symptoms associated with it. However, methods of reversing or preventing the damage associated with I5 such dietary-induced liver damage have not as yet been available. These conditions are not generally cleared by the administration of choline.
Another dietary-related malady resultant from abnormal lipid mobilization and deposition is dietary hypocholesterolemia. High cholesterol diets (high concentrations of dietary carbohydrate or triacylglycerol) in animals have been shown to result in the formation of fatty deposits at multiple tissue sites, particularly on the heart, liver and large arteries.
Methods of treating these conditions are relatively non-existent, while any method for providing the regeneration of damaged liver tissue is at this time unknown.
The condition of hypercholesterolemia has been primarily observed in persons consuming high cholesterol-containing diets or diets which include high ethanol concentrations. The predominant lipid fraction in an ethanol compromised liver is triglyceride.sup.1-5. However, significant increases in the levels of cholesterol esters and cholesterol.sup.1-7, phospholipids.sup.2-6, and lipoproteins have been reported.sup.7.
Although a high fat diet accentuates fatty infiltration of the liver.sup.8, endogenous biosynthesis of fatty acids is the main cause of hepatic steatosis in chronic alcoholism.sup.2,9,10, This alteration is further aggravated by impaired oxidation of fatty acids in an ethanol compromised liver.sup.11. The explanation for the ethanol induced increase in hepatic deposition of fat is still not very well understood. However, most investiqators believe that ethanol inhibits hepatic fatty aoid oxidation which secondarily causes fatty acids to be stored as triacylglycerol.
Recent studies of Kosenko and Kaminsky.sup.12 demonstrated that ethanol consumption decreases the [NADP]/[NADPH] ratio in non-fasted rats, and both ethanol withdrawal and fasting in ethanol ingesting animals appears to increase the ratio to normal or higher levels. Ethanol has also been shown to decrease total hepatic [NAPD]/[NADPH] ratio upon chronic ingestion in the rat.sup.13. In other studies on the hepatic redox state, ethanol was reported to decrease the free cytosolic and mitochondrial [NAD]/[NADH] ratios.sup.14,15.
Fatty liver as a concomitant of the ingestion of high fat diets, alcohols or chlorinated hydrocarbons is a well-known phenomenon. Chronic intake of ethanol results in, among other things, hepatic injury to the accumulation of triglycerides and eventually, cirrhosis. Acute alcohol ingestion in man has not clearly been associated with alteration of hepatic function; however, in chronic ethanol ingestion as well as ethanol withdrawal are factors affecting the activities of NADPH-generating enzymes and their quantitative contribution to an ADPH-generation in liver. Furthermore, the variation of hepatic [NAD]/[NADH] ratio occurs in ethanol treated rats, which is a function of both ethanol dose and time following its administration.sup.16. It has been suggested that the elevated concentration of NADH creates conditions favoring increased lipid synthesis and that the latter contributes to the development of fatty livers in chronic alcoholics.sup.17,18.
A triglyceride concentration in the range of 200-800 mg/dl with a normal or near normal cholesterol concentration almost always indicates a simple elevation of VLDL. Triglyceride concentrations greater than 1,000 mg/dl usually indicate the presence of chylomicrons, either alone or in addition to elevated VLDL. Circulating LDL constitutes the major reservoir of cholesterol in human plasma, accounting for 60 to 70% of the total. When liver or extrahepatic tissues require cholesterol for the synthesis of new membranes, steroid hormones, or bile acids, they synthesize LDL receptors and obtain cholesterol by the receptor-mediated endocytosis of LDL. Conversely, when tissues no longer require cholesterol for cell growth or metabolic purposes, they decrease the synthesis of LDL receptors.
In addition to degradation by specific receptors, lipoproteins are also disposed of by less specific pathways, some of which operate in macrophages and other scavenger cells. When the concentration of lipoprotein in plasma rises, the rate of its degradation by such pathways increases. This contributes to the deposition of cholesterol in such abnormal locations as arterial walls (producing atheromas) and of macrophages in the tendons and skin (producing xanthomas).sup.19.
A diet with reduced cholesterol and fat are effective in the clinical management of some forms of high-blood lipid conditions. For example, Anitschow demonstrated that some regression of cholesterol-diet induced atherosclerotic lesions were evidenced by the maintenance of animals on a normal diet for periods ranging from 18 to 24 months.sup.27.
Other studies have shown that r.RTM.duction of dietary-induced lesions after restoration of normal diets in rabbits (and other animals) could be accelerated and markedly enhanced when the normal regimen is supplemented by feeding chelating agents.sup.27, by production of hyperoxemia.sup.28, by combination of cholestyramine and hyperoxemia.sup.29, by a combination of diphosphonate and colchicine.sup.30, and by clofibrate.sup.31.
An important feature in the development of atherosclerotic lesions is the injury to the endothelium and the change in endothelial permeability to various blood materials. Materials contained in the blood subsequently pass through those compromised endothelial tissues and into the intima of the arterial wall. It has been demonstrated that even a moderate increase in endothelial permeability is accompanied by a significant increase in the incidence of atherosclerotic events.sup.26.
Despite the intense work in this area of medical research, atherosclerotic disease, such as arteriosclerosis, remains a significant medical problem. The high incidence of diets rich in fat exacerbate even the mildest of artherosclerotic conditions over time. Secondary physiological effects, which often accompany the onset of such atherosclerotic maladies, include sub-optimal liver function. Unfortunately, diet induced liver disease is clinically treated as irreversible tissue damage.
Diet is not always effective in the management of all or most forms of hypercholesterolemia or hypertriglycemia. Many therapeutic agents currently on the market have been used where diet is ineffective to control abnormally high blood lipid levels, as well as the secondary maladies high blood lipid concentrations cause.
Abundant circumstantial evidence indicates that treatment of hyperlipoproteinemia will diminish or prevent atherosclerotic complications. As a result, several pharmaceutical agents have been developed to t:reat these conditions. The most widely known of these agents include nicotinic acid (a particular methylxanthine compound), Ronitol (which has an alcohol which corresponds to nicotinic acid), clofibrate (atromid-S), Gemfibrozin (for treatment of hyperlipoproteinemia, a structural congener of clofibrate), compactin and mevinolin (HMG CoA reductase inhibitors - are fungal metabolites), Choloxin.RTM., (i.e., dextrothyroxine -( sodium), Neomycin (oral administration only hypolipidemic effect - reduces LDL), beta-sitosterol (a plant sterol -lowers LDL, not VLDL), and probucol (4,4'-(isopropylidenedithiol)-bis(2,6-di-t-butylphenol).sup.20.
Nicotinic acid was discovered as a hypolipidemic drug in 1955.sup.21. Specifically, nicotinic acid acts to reduce elevated concentrations of VLDL and its daughter particles, LDL and IDL. While pharmacological doses of nicotinic acid are useful in the treatment of most forms of hyperlipoproteinemia, such is limited by the frequent occurrence of a constellation of side effects. The side-effects normally attendant such use include intense cutaneous flush, pruritus increased arterial fibrillation, gastrointestinal irritation, hepatotoxicity, and other cardiac arrhythmias.
Additionally, the side effects associated with nicotinic acid results in poor patient compliance with prescribed doses. Beneficial effects reported from prolonged nicotinic acid administration include the regression of eruptive, tuboeruptive, tuberous and tendon xanthomas. Niacin (nicotinic acid) is contraindicated in patients when hepatic dysfunction, which is an almost certain concomitant of hypercholesterolemia. Consequently, nicatinic acid is contraindicated in those patients with hepatic dysfunction.
While nicotinic acid does not produce any detectable changes in total body synthesis of cholesterol it significantly alters the excretion of bile acids in man.sup.22. Additionally, it is known to inhibit lipolysis in adipose tissue, decrease esterification of triglycerides in the liver, and to increase the activity of lipoprctein lipase.sup.23.
Clofibrate has been described as the one of a series of aryloxyisobutyric acids which are effective in reducing plasma concentrations of total lipid cholesterol with minimal toxicity However, questions recently have arise as to its actual effectiveness.sup.24. This, together with its now recognized latent adverse effects, have circumscribed its use to almost exclusively the treatment of familial dysbetalipoproteinemia (type-III hyperlipoproteinemia). It has also occasionally been useful in patients with severe hypertriglyceridemia as a last resort in patients who do not respond to nicotinic acid or gemfibrozil. Chemically, clofibrate is the ethyl ester of p-chlorophenoxyisobutyric acid.
In the treatment of familial dysbetalipoproteinemia, the use of clofibrate results in a significant reduction of cholesterol and mobilization of deposits of cholesterol in tissues, accompanied by regression and disappearance of xanthomas. Clofibrate has no effect on hyperchylomicronemia, nor does it affect concentrations of HDL (except in some hypertriglyceridemic subjects in whom marked reduction of VLDL may be accompanied by modest increments in HDL).sup.20. Side effects associated with clofibrate include nausea, diarrhea, weight gain, skin rash, alopecia, impotence and a flu-like syndrome. The flu-like syndrome, where it does occur, is also associated with severe muscle cramps and tenderness, stiffness and weakness. Cholelithiasis and cholecystitis have also been associated with this drug by the enhancement of particular enzymes.
Clofibrate is contraindicated for patients with cardiac artery disease, owing to the risk of drug-induced cardiac arrhythmia, cardiomegaly, increased angina, claudication and thromboembolic pneumonia.sup.20.
Gemfibrozil has been used for the treatment of hyperlipoproteinemia, and is a structural congener of clofibrate. It has been shown to be effective in reducing the plasma concentration of VLDL in hypertriglyceridemic patients who do not respond to diet. Gemfibrozil has also been shown to raise plasma concentrations of HDL. The drug has shown only limited ability to reduce LDL, as plasma LDL-cholesterol has been reported as reduced by less than 10% in hypercholesterolemic patients.sup.20. However, clinical evidence of this drug is limited, and its long-term safety has yet to be established.
Gemfibrozil has been shown to inhibit lipolysis of stored triglyceride in adipose tissue and to decrease the uptake of fatty acid by the liver.sup.25. Side effects associated with its use include gastrointestinal distress, abdominal pain, diarrhea, nausea, eosinophilia, skin rash, mucoskeletal pain, blurred vision, mild anemia, leukopenia, and the enhancement of gallstones.
Probucol has been demonstrated to cause a: moderate reduction in plasma concentrations of LDL-cholesterol. Probucol has several properties that set it apart from other lipid-lowering drugs. Two of these properties may limit its clinical utility. For example, it is a highly hydrophobic compound, and it thus persists in adipose tissue for months after patients stop taking it. Additionally, it has been shown to cause a substantial lowering of plasma HDL-cholesterol concentrations in addition to its effects on LDL.sup.20. Long-term effects of the drug are not yet known.
Probucol has no apparent structural similarity to other agents that lower cholesterol concentrations. It is a sulfur-containing bis-phenol. The known effects on plasma concentrations of VLDL and triglycerides are minimal. Side effects of this drug include diarrhea, flatulence, abdominal pain, and nausea.sup.20. Fatal cardiac arrhythmias have also been shown in experimental animals that have received a diet high in cholesterol and saturated fat. It is medically advised that probucol be reserved for the treatment of hypercholesterolemia in patients with excessive plasma LDL concentrations who cannot be controlled with dietary management and more conventional drugs. Additionally, because of its potentially undesirable effect in lowering HDL concentrations, probucol is not widely recommended, and is not known to benefit patients with hypertriglyceridemia. There is, as yet, no evaluation of the efficiency of probucol for the prevention or control of atherosclerosis or its clinical sequela.
Cholestryamine is a chloride salt of a basic anion-exchange resin. Cholestipol hydrochloride is a second of these bile-acid binding resins which is a copolymer of dimethyl pentamine and epichlorohydrin.sup.20. These bile-acid binding resins characteristically reduce the concentration of cholesterol in plasma by lowering the level of LDL, usually to about 20%. In most patients, reported concentrations of triglyceride in plasma (VLDL) increase by 5 to 20% initially and then returns to normal. Body pools of chclesterol are reportedly decreased after long-term therapy with bile acid-binding resins, and there has been some regression of xanthomas reported.sup.20.
Side effects of these drugs include nausea, abdominal discomfort, indigestion, constipation, and impaction.
Compactin and mevinolin are two M/HMG and CoA reductase inhibitors which chemically differ from each other only by one methyl group. They both resemble HMG CoA, the natural substrate of HMG CoA reductase. Mevinolin is currently under study in the United States as an investigational drug. It is medically recommended that until the long-term safety of mevinolin and compactin is established, use of these drugs should be reserved for the experimental treatment of patients with the heterozygous form of familial hypercholesterolemia. These agents are not useful for the treatment of hypertriglyceridemia.
Choloxin (dextrothyroxine sodium) is the original isomer of the hormone, L-thyroxine. Plasma concentrations of VLDL and HDL are not changed significantly. Side effects associated with this drug include an increase in frequency or severity of anginal attacks in patients with coronary heart disease, cardiac arrhythmias, nervousness, sweating, tremor and insomnia. The use of this drug is medically recommended to be restricted to young patients with familial hypercholesterolemia or polygenic hypercholesterolemia, who are known to be free of coronary artery disease and who do not respond to diet and more conventional drugs.
It is clear that extensive research and interest in the treatment of those physiological conditions precipitated from high dietary fat and cholesterol ingestion (postulated to precipitate atheromatous lesions, fatty deposits, and more specifically, fatty cirrhosis of the liver) exists. However, there remains to be elucidated more effective methods for reducing circulating lipids without the multiple side effects of conventional blood lipid-reducing drugs. Additionally, a method is still needed which would both treat and reverse the tissue damage associated with such lipid deposits. The development of a method which would actually regenerate lipid and alcohol-related tissue damage, such as those attendant cirrhosis of the liver, would provide a major advancement in the clinical management of patients with diet-compromised liver function and morphology.
Pentoxifylline is a methylxanthine which is an FDA approved pharmaceutical agent. It has been used as a peripheral vasodilator in the treatment of intermittent claudication.sup.32. Several derivatives of theobromine have also been synthesized and tested for potential use in the treatment of peripheral vascular and cardiopulmonary diseases. A water-soluble derivative of theobromine similar to pentoxifylline, [1-.beta.-hydroxypropyl substitution instead of 1-5- oxo hexyl substitution], has been shown to be an effective bronchodilator when administered by aerosol inhalation.sup.33. However, the systemic vascular effects of this hydroxypropyl derivative have not yet been examined.
Pentoxifylline has the following chemical name: 1-[5-oxohexyl]-3,1-methylxanthine. Its structural similarities to the methylxanthine contained in beverages are as follows: triple 1,3,7 substitution like caffeine; 3,7-dimethyl substitution similar to theobromine and in contrast with 1,3-dimethyl substitution of theophylline. As a pharmaceutical agent, PTX has been prepared in a mixture with a saliva forming agent.sup.34 to enhance the agent's biocompatibility with the gastrointestinal tract of a patient.
Pentoxifylline has been demonstrated to have particular cardiac effects, such as enhanced cardiac output.sup.35. However, clinical studies supporting the efficacy of orally administered pentoxifylline show no effect on heart rate, blood pressure and cardiac output. The effect of pentoxifylline is not active or musculotropic vasodilation, in contrast with the effect of the methylxanthine, aminophylline.
Most patients followed in pentoxifylline clinical studies were also suffering from non-diabetic forms of arteriosclerosis obliterans, Buerger's disease or varicose veins, and were clinically evaluated after intravenous, intramuscular or intra-arterial injections of pentoxifylline. The initial observations following the intravenous injection of pentoxifylline suggested an improvement of blood flow to ischemic limbs in patients with intermittent claudication.
An increase in microcirculation of ischemic leg tissue is described as resulting from pentoxifylline-induced alterations in flow properties of the blood in general, and of erythrocytes in particular. This effect also results in an improvement in oxygen supply to the muscles. Ehrly and colleagues have explained the improvement in oxygen supply to the muscles as a result of improved erythrocyte flexibility and increase in microcirculation.sup.36. Overwhelming evidence supports the proposition that improvement in capillary blood flow is brought about by increasing erythrocyte flexibility, both of which are reduced in patients suffering from intermittent claudication.
Another significant effect of pentoxifylline treatment is a reduction in plasma fibrinogen level. A reduction in plasma fibrinogen level may reduce blood viscosity severely enough to cause bleeding reactions. It is not yet possible to define the importance of improved red cell flexibility relative to that of reduced plasma fibrinogen level in effecting a reduction in whole blood viscosity.
Other effects of PTX have been shown to include the reduction of antiplasmin activity.sup.37 elevation of plasminogen concentration.sup.38 inhibition of platelet aggregation.sup.39 enhancement of fibrinolytic activity.sup.40 stimulation of prostacyline production in the endothelial cells of the vessel wall.sup.41 and elevation of platelet CAMP concentration.sup.42.
Complications of cardiovascular disease are the major cause of death in most industrial countries, with
atherosclerosis being the primary physiological process associated with this mortality.sup.43. A method for reducing and reversing lipid deposition believed to precipitate the tissue damage (e.g. xanthomas lesionary), without patient-deterring side effects would present a substantial advancement in the treatment of an ever growing health problem.
The development of a method using currently acceptable pharmaceutical agents for the treatment of these fat, alcohol, and other diet-related maladies would present a significant step in the rehabilitation and cure of these and other high lipid and/or ethanol diet-induced conditions.